Perlite

Inert growing media - mineral wool, expanded clay, perlite
The common feature of all inert media is the diverse application not only in gardening and cultivation. Their advantages include mainly absorption and retention abilities. Inert means indifferent, unresponsive.

Perlite - substrate supplement
Perlite is a volcanic glass with an irregular (amorphous) structure that commonly occurs in nature. It has a high volume of water, is inert, does not react with other substances. At high temperatures (above 850 degrees Celsius) it gets rid of water and at the same time dramatically increases its volume. The advantages of white, industrially produced perlite include retention and aeration capabilities, fully usable in the home cultivation of various members of the plant kingdom. Like expanded clay, perlite does not harm the environment and is a frequent admixture of soil mixes and other types of non-inert substrates.